Water heater, turn off or leave on?

JLA · 13-11-2009, 1:29 PM

Hi,

I have just moved to a new apartment that has a water heater fitted. I have not used one before and would like to know if I turn it off while im at work and turn it on overnight would this be better than leaving it on all the time?

At the moment I turn it on around 10pm and off at 8.30am when i leave for work, when i arrive back home at 5.30pm the water is still hot all thought the afternoon so i do not need to turn it back on.

Do you think this is causing me to use more electricity or am i doing the right thing?

thank you for your time to reply

shahedz · 15-11-2009, 11:07 AM

Do you know what type of hot water tank you have?

I have an unvented direct cylinder with remote expansion vessel. These are very efficient and allegedly its cheaper just to leave on 24/7. They have a thermostat so just click on and off to maintain the water temp.
To tell if you have the above its a big hot water tank that is then connected to a smaller little tank. It's also very cool to touch.

The ones that are traditional hot water tanks tend to lose heat and are not so efficient so cost more to run. These all tend to have timers.

I would think if its fairly new with out one its an unvented one and doesn't require a timer.

neilball · 15-11-2009, 11:30 AM

Even if the tank is well insulated it will still loose some heat and leaving it turned on 24/7 means that it will remain at a higher temperature for longer thereby loosing more heat then when it is cooler (but still hot enough for you to use). If you are having to manually switch the heater on & off I would suggest getting a timeclock fitted so you don't have to keep switching it all the time.

When you use the hot water the energy to heat it up remains the same whether this happens immediately (24/7 running) or later (timed/manual switching) so the only wastage or savings are by reducing the standing losses when you are not at home.

Assuming the tank is electrically heated and if you want an absolute answer then consider getting an energy monitor such as the CurrentCost CC128 and try each method on alternate days, the CC128 will tell you how much energy you used over 24 hours so you can compare the actual amount to see for yourself.

JLA · 15-11-2009, 1:44 PM

Thank you for your replies,

i am a private tennant, and the building is only 5yr old so fitting a timer or enery monitor ill have to get permission from the landlord.

the water heater i have is OSO direct 20 RD 170 ltr and is 3.0kw unvented

i cannot see an external expansion vessle and the switch i am using to turn it on/off is a fuse spur inside the cupboard next to the unit. The unit itself is very cool to touch.

sorry about spelling/grammar i have no internet yet so am using my phone to reply.

thank you for your time

shahedz · 15-11-2009, 3:12 PM

for my tank, i was told by a few people , keeping the tanking ticking over at one temp was more efficient than heating up a tank, letting it cool down than having to heat it all up again.

My apartment was built about 6 years ago. It really focused on energy efficiency etc and CO2. It's very well insulated, and even has a Air Source Heat pump fitted as standard ( these are super efficient and use 30-40% energy a standard boiler would use). I thought it was really odd that they focused on all these measure for efficiency and cutting energy costs and then not have a timer on the hot water tank. That's when i investigated more and was told by a few sources its more efficient just to leave it ticking over.

shahedz · 15-11-2009, 3:16 PM

neilball- that monitor you recommended looks great.

I'm thinking of getting one but my main problem is my electricity meter is down the hall way. The consumer unit is in my flat. Does this need to go round the meter or consumer unit ( the sensor)

thanks

neilball · 15-11-2009, 8:35 PM

The sensor is most easily fitted at the meter and is battery powered. It then transmits wirelessly to the display unit - my sensor/transmitter is in my meter cupboard which is built in to the external wall of my detached garage and the display sits inside my house. I don't have any problems with the display picking up the transmitter.

Your other alternitive depends on the accessibility of the cabling at your main consumer unit/fuse board - if there is enough room you may be able to fit the sensor here although it can only be placed around the live conductor, it will not work if it is placed around live & neutral.

shahedz · 15-11-2009, 8:53 PM

Thanks Neil

Will check my consumer unit.

Shah

m4rky_m4rk · 17-11-2009, 7:11 PM

Quote:

Originally Posted by shahedz

for my tank, i was told by a few people , keeping the tanking ticking over at one temp was more efficient than heating up a tank, letting it cool down than having to heat it all up again.

This reminds of my arguments with my ex. I could not convince her that its cheaper to run if you let it cool down....

Hot things loose energy (money) much faster the hotter they are. In fact I think heat energy loss is directly proportional to the relative temperature of the tank to its surroundings. eg If the tank of water was as cold as the room its in then it can't loose any more heat therefore costs nothing to keeping ticking over at room temperature. Heating it up to working temperature from cold isn't wasting money because the energy used to heat it up is stored in the water and you get it back later in the form of hot water. Only the lost heat through the insulation is costing money because that's wasted heating the room up, and the hotter the water is the faster it will be loosing energy (money) to its surroundings.

Heating a tank of water is not analogous to a motor car, were cruising at steady speed is the most economical way to travel.

Have I still failed to convince?

Educated Guess · 17-11-2009, 7:38 PM

Asked the exact same question myself some time ago HERE

Never did get a definitive answer and it's a question that still bugs me.

I always turn the water off during the day/night and only heat it a few hours before needed (it's on a timer). If it's on all day as far as I'm concerned it's wasting energy.

m4rky_m4rk · 17-11-2009, 8:14 PM

Another way to look at it. If the tank wasn't loosing energy while its hot then once heated the water would never cool down. The fact that it does cool down is because of the heat losses and these are higher the hotter the water is. eg if the tank is at 100C it will cool from 100 to 80c faster than it would from say 80 to 60. Its a cooling curve and not a straight line.

Heating the water up isn't wasting energy because that energy is stored in the water making it hot. The biggest losses are keeping the water hot.